The present invention relates to the field of fluid control valves, in general, and more particularly to electrically controlled, shape memory alloy element actuated fluid control valves.
In general, manufacturing processes, like those involved in the semiconductor industry, for example, use fluid control valves in the liquid or gas delivery systems thereof. Typically, these valves are either pneumatically controlled or hydraulically controlled. A present obstacle in the use of the fluid control valves is the surge of flow associated with the rapid opening of the valve. The resulting turbulence and rapid pressure rise in the exiting fluid is undesirable for other system components. For example, in the semiconductor industry such turbulence and rapid pressure rise can cause particle xe2x80x9cstir upxe2x80x9d that can lead to contamination deposits on the wafers, which causes high rejection rates (i.e., low yields). As a result, several different methods have been used to better control the rate of opening of the valve. Among these are the use of a variable orifice which allows the valve piston to be driven at a slower rate, the use of a solenoid to control the flow of the fluid to the air operator, and the use of a metering valve to limit the fluid flow in the delivery system.
Recently, electrically driven fluid control valves utilizing a shaped memory alloy (SMA) drive element have been proposed for use in the fluid delivery systems of manufacturing processes. Shape memory alloys are materials that are capable of large and repeatable phase-transformation induced strains. One such valve integrates a single shape memory alloy wire into its valve housing within the biasing spring portion thereof. As proposed, the single SMA wire is essentially a rod having a diameter of approximately one-quarter of an inch. A special power supply with low voltage and high current requirements would be required to heat such a large diameter/mass of wire or rod. In addition, once heated the large mass of material would cool very slowly resulting in an undesirable slow closing of the valve. Another type of SMA driven fluid control valve provides for an SMA wire wrapped around the body of the valve but still integral to the valve. Both of these types provide for, mechanically active SMA wire terminations which may lead to mechanical and/or electrical malfunctions. None of these proposed SMA actuated fluid control valves appear to offer commercially viable solutions to the aforementioned concerns with pneumatically or hydraulically driven fluid control valves presently used.
The present invention includes aspects which overcome the drawbacks of the prior proposed SMA actuator fluid control valves and offers further aspects not as yet considered in the prior art.
In accordance with the present invention, a fluid control valve having a shape memory alloy (SMA) driven actuator comprises a valve body including a movable element positionable in relation to the valve body to control fluid flow from an inlet port to an outlet port therethrough; a bias means for forcing the movable element to a first position; and a valve actuator including a first frame section coupled to the valve body and fixed in relation thereto; a second frame section coupled to the movable element and movable in relation to the valve body; and a multiplicity of SMA wire sections coupled between the first and second frame sections for moving the movable element from the biased first position to a second position when heated. The valve may further include an electrical controller for controlling the heating of the SMA wire sections by regulating current therethrough. The valve actuator may be enclosed within a housing which includes openings for allowing air to flow through the valve actuator.
In accordance with another aspect of the present invention, an electrically controlled fluid control valve includes a position measuring element for providing a measurement proportional to the position of the movable element, and an electrical controller governed by the position measurement to regulate current to the SMA drive element to position the movable element to a desired position. In one embodiment of this aspect, the position measuring element is integral to the valve actuator and comprises oppositely disposed conductive plates that are part of the valve actuator assembly and that form a capacitive element, the capacitance of which changing in proportion to the position of the movable element. The electrical controller includes means for sensing the capacitance of the capacitive element and converting it into an electrical signal representative of the position of the movable element.
In yet another aspect of the present invention, a temperature compensated, electrically controlled fluid control valve includes a temperature sensing means disposed in proximity to the SMA drive element to measure temperature and generate an electrical temperature signal representative thereof, cooling means for reducing the temperature surrounding the SMA drive element when activated, and a temperature controller governed by the electrical temperature signal to activate the cooling means. In one embodiment of this aspect, the cooling means may be selected from the group consisting of a rotary fan, a Piezo-fan cooling device and a Peltier cooling device. In another embodiment of this aspect, the temperature controller activates the cooling means as a function of the electrical temperature signal and a temperature setpoint.
In yet another aspect of the present invention, an electrically controlled fluid control valve includes a means for selecting a rate of heating the SMA drive element, and an electrical controller governed by the selecting means to regulate current to the SMA drive element. In one embodiment of this aspect, the electrical controller includes means for regulating current to the SMA drive element by pulse width modulation of the current. In another embodiment of this aspect, a digital selector switch is used for generating a digital code representative of the selected rate. In this embodiment, the electrical controller is a digital controller governed by the digital rate selection code to modulate the current to the SMA drive element.
In yet another aspect of the present invention, the electrical controller of the fluid control valve is governed by both the position measurement and the temperature signal to regulate current to the SMA drive element and to control the cooling means to position the movable element to a desired position. In one embodiment of this aspect, a first means is governed by the position measurement and a position setpoint to generate a temperature setpoint, and a second means is governed by the temperature signal and the temperature setpoint to regulate current to the SMA drive element and to control the cooling means to position the movable element to a position represented by the position setpoint. In another embodiment of this aspect, the second means regulates current to the SMA drive element based on a difference of the temperature setpoint and temperature signal of one plurality and controls the cooling means based on a difference of the temperature setpoint and temperature signal of the other polarity.
In yet another aspect of the present invention, a method for configurating a bobbin of non-conductive material wound with a multiplicity of SMA wire windings for a SMA driven valve actuator comprises the steps of removing groove sections from the bobbin for acceptance of the multiplicity of SMA wire windings, applying a conductive material to the surface area of the grooved sections, and winding the SMA wire windings onto the conductive grooved surfaces. In accordance with yet another aspect of the present invention, a method for preparing the SMA wire for an SMA driven valve actuator comprises the steps of coating the SMA wire surface with a conductive material, and winding the coated SMA wire around the at least one bobbin, and removing the conductive material from the surface of the SMA wire not in contact with the at least one bobbin.